1. Field of the Invention
The present invention relates to feedwater spargers in boiling water reactors and, more particularly, to clamps for the end bracket assemblies of feedwater spargers.
2. Description of the Related Art
While the present invention may be used in a variety of industries, the environment of a boiling water reactor (BWR) nuclear power plant will be discussed herein for illustrative purposes. In a BWR, a steam-water mixture is produced when reactor coolant (water) moves upward through the core, absorbing heat produced by the fuel. The steam-water mixture leaves the top of the core and enters a moisture separator, where water droplets are removed before the steam is allowed to enter the steam line. The steam line directs the steam to the main turbine, causing it to turn the turbine and the attached electrical generator. The steam is then exhausted to a condenser where it is condensed into water. The resulting water is pumped out of the condenser back to the reactor vessel as feedwater. Recirculation pumps and jet pumps allow the operator to vary coolant flow through the core and change reactor power.
Within the BWR vessel, core shrouds surround the core to provide a barrier to separate the downward coolant flow through the annulus/downcomer (the space between the core shroud and the reactor vessel wall) from the upward flow through the core and fuel bundles. The feedwater is injected through nozzles in the reactor vessel and distributed by feedwater spargers. The feedwater spargers are located inside the reactor vessel and include a central T-connection with two pipe branches that are curved concentric with the inside radius of the reactor vessel. Each curved pipe has a set of nozzles through which the feedwater is injected.
Each curved pipe has an end bracket that is welded to the pipe. The end brackets are C-shaped and surround an attachment lug that is welded to the reactor vessel wall. Pins having relatively large diameter heads are inserted through the end brackets and the attachment lug. Each pin has a securing nut on the bottom that is installed tightly against a shoulder of the pin but allows a gap between the nut and the bottom of the end bracket white the head of the pin rests against the top of the bracket. The sparger end brackets are secured axially to the attachment lug, but the end brackets are slotted to allow for relative thermal expansion and contraction of the feedwater sparger assembly. FIG. 7 shows a partially cut-away isometric view of a typical sparger end bracket assembly, including the pin 2 and bracket 3.
Visual inspection of the spargers has revealed wearing of the end brackets and pin heads. The wear is caused by vibration of the pin relative to the bracket, which is believed to be caused by flow induced vibration.